1. Field of the Invention
The present invention relates to an electrical component with a PTC polymer element. Such components are known, for example, from EP 0 655 760 A2, according to which a PTC polymer element is used for overcurrent limitation and, for this purpose, the PTC polymer element is connected in series with a load interrupter. A current above a threshold value, determined by the design of the PTC polymer element, in this case produces a rapid non-linear rise in the electrical resistance of the PTC polymer element and thereby limits the overcurrents. The load interrupter can then completely interrupt the limited current.
2. Discussion of Background
With respect to the use of PTC polymer elements at relatively high voltages, various possibilities have been proposed in U.S. Pat. Nos. 5,313,184 and 5,414,403 for using resistance systems comprising PTC polymer elements and varistor elements or linear resistor elements for reducing local overvoltages in the PTC polymer material and locally distributing the non-linear response behavior of the PTC polymer material. In connection with the teaching of these two documents, it can be stated that in the case of the present invention the terms PTC polymer element and PTC polymer material definitely also cover such elements and materials to which constituents without PTC behavior, for example linear resistor elements or varistor elements, are added.
Furthermore, this invention relates to such an electrical component in which the PTC polymer element does not have a constant current-carrying cross-sectional area, but instead the line cross-sectional area is constricted. The main direction of flow defining this cross-sectional area is generally dictated by external contacts on the PTC polymer element or by the geometry. At the same time, however, it does not have to correspond to all local directions of flow occurring, but to a certain extent only to their mean value.
Such a constriction of the line cross section has the effect that the current density in relation to the remaining PTC polymer element is locally increased, so that it is predetermined at which point the non-linear rise in resistance of the PTC effect begins when corresponding current threshold values are reached.
EP 0 798 750 A2 in turn shows a resistance system comprising a PTC polymer element with varistor elements in which such constrictions are provided.
U.S. Pat. No. 3,351,882 likewise shows PTC polymer elements with constrictions, giving as the reason for this that, by suitable choice of the constrictions, overheating in the vicinity of the contact points of the PTC polymer element is to be avoided.
Also to be cited as prior art is European Patent EP 0 038 715 B1, in which a very rapid response behavior in the range of a few seconds or less is to be achieved by a specific design of a PTC polymer element with a constriction.
A PTC polymer element with a constriction is also shown, furthermore, by JP 4-130602 with Patent Abstract, DE 196 26 238 A1 as well as U.S. Pat. Nos. 4,317,027 and 4,352,083. The two last-mentioned documents also show in particular that constrictions can be formed by neighboring recesses in a PTC polymer material. In this case, the recesses are filled with an essentially non-conducting material or with air.